[expert] Missing RAM - an old chestnut

[Glyn Millington]

This is an old question but for me its a new machine.  

It's an AMd K6 450 with 32 mb RAM (soon to be increased!)

On firing up Mandrake 7 (with kernel 2.2.15-0.18mdk), it tells me
I have 23MB ram.  I've added
append =  "mem=32m" 
to lilo.conf with no effect.
Can anyone tell me what is going on here?
Is Linux not detecting the RAM?
Is it discounting space used by the kernel?

I've trawled the docs but couldn't find any clues.

TIA

Glyn M.
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